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How Python Compares Floats and Ints: When Equals Isn’t Really Equal
(blog.codingconfessions.com)
this post was submitted on 27 May 2024
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Unfortunately, that's not what it's about.
With Rust's language design¹, one could easily forbid ever comparing two floats via the normal operators (not just for literals), but they decided to allow that nonetheless. I'm guessing, because it would just be too annoying for generic implementations, if you'd always need special treatment for floats.
Rather, what I was referring to, is that they've split partial ordering and partial equality from their total variants. And integers are marked that they can do total equality and total ordering, whereas floats are not.
Honestly, it doesn't come up a lot, but I know for example, if you want to use something as a key in a HashMap, it needs to have total equality.
And in a BTreeMap (basically a binary tree, i.e. keys are inserted in a sorted manner), total ordering is required for the keys.
¹) Basically, comparison is typed and each type needs to opt into comparison with any type it wants to be compared to. So, if you define a new data type, then by default you cannot ask it whether it's equal to or less/more than anything else.